In many fields of communication between two or more computers such as those used in military avionics, tanks, howitzer systems and the like wherein digital and analog information must be processed between computers, it has been a common practice to drive the inputs of a transmitter section of one transceiver with digital data which is then appropriately processed in the transmitter and used in turn to drive an output transformer. This output transformer may be connected in one of several available transformer configurations, and the output transformer is in turn connected to a standard bus line and data link and is operative to convert the digital data to an analog voltage of a specified wave shape, waveform timing and power level. These later parameters must be sufficient to properly transmit the analog data from the transceiver over the bus line and to a similar transceiver located at a remote computer within the particular communication system.
For example, in certain military aircraft avionics systems, there might be one such computer in the aircraft cockpit to provide pilot information from another remotely located computer operative for providing various aircraft operational parameters such as speed, direction, fuel levels, temperatures, wind velocities and the like. These two physically separated computers would therefore each be equipped with one or more transceivers which are connected over relatively short data bus links typically on the order of 300 feet or less.
In the past, it has been a common practice to use several hybrid connections in the fabrication of a transceiver of the type described above. This practice required that a common insulating substrate such as a ceramic material be used to support and provide electrical interconnections between various components on the substrates such as one or more integrated circuit die, discrete capacitors, thin film resistors, and the like. The requirement for these hybrid circuit interconnections and associated fabrication assembly processes had the disadvantage of providing the additional space required to accommodate the substrate size, and more importantly the disadvantage of increased production costs and decreased device reliability associated with these hybrid fabrication and interconnection processes.
Another common practice used in the fabrication of these prior art transceivers was to provide a 15 volt DC power supply in order to minimize the current drive levels necessary for properly driving the output transformer of the transmitter section of the transceiver at the above specified wave shapes, waveform timing, and analog signal power levels on the bus lines to which the transformer was connected. The disadvantage of using this relatively high level DC voltage supply of 15 volts is that a separate 15 volt supply voltage is required in addition to the standard 5 volt Vcc voltage used for powering the standard monolithic integrated circuits which are already contained in a sub-system. This requirement in turn added cost to the sub-system and has been generally objectionable to system and sub-system designers.
More particularly, for certain transceiver applications such as the military standard 1553 (MIL-STD-1553) avionics bus line for interconnecting computers, it has been specified by some sub-system manufacturers that the transceiver must operate off of a 5 volt DC power supply. This requirement has made the task of bringing all of the components heretofore constructed in hybrid form into a single monolithic die extremely difficult. Furthermore, the requirement for using a single 5 volt Vcc supply voltage in turn means that parts of the monolithic die must be driven below ground (i.e. the silicon substrate potential) in order to produce the necessary transformer output current drive waveforms for the transmitter section of the transceiver. This latter mode of operation was not heretofore required when using 15 volt DC voltage supplies. This latter requirement for driving the silicon substrate below ground in turn introduces a myriad of problems into the transistor switching process used in the transceiver.
As one example, using a 15 volt DC supply with a grounded substrate, it was hitherto a common and preferable practice to use complementary driven high speed NPN driver transistors and vertical PNP transistors to provide the high speed signal processing and transformer switching action for the transceiver. However, when one is limited to using a single 5 volt Vcc DC supply, there has been much skepticism among those skilled in the art that the required timing, speed, and power output and impedance requirements for the MIL-STD-1553 data bus could be maintained with an all monolithic transceiver, particularly since vertical PNP transistors and output NPN transistor drivers frequently cannot be properly maintained in their "off" state when driven below substrate potential. This characteristic would therefore require the use of an NPN output transistor with a PNP driver transistor. If a vertical PNP transistor is not available, a lateral PNP transistor needs to be used as the driver transistor, and these lateral PNP transistors were not believed to be capable of maintaining the above required timing, speed and power requirements for the MIL-STD-1553 avionics system transceivers.